Disregard synthetic definitions from experimental imports checks

Author: odersky

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -727,7 +727,7 @@ object Checking {
   def checkExperimentalImports(trees: List[Tree])(using Context): Unit =
     def onlyExperimentalDefs = trees.forall {
       case _: Import | EmptyTree => true
-      case stat: MemberDef => stat.symbol.isExperimental
+      case stat: MemberDef => stat.symbol.isExperimental || stat.symbol.is(Synthetic)
       case _ => false
     }
     for case imp @ Import(qual, selectors) <- trees do

tests/pos/experimental-erased.scala

@@ -2,5 +2,14 @@ import language.experimental.erasedDefinitions
 import annotation.experimental
 
 @experimental
-erased class CanThrow[-E <: Exception]
+erased class CanThrow[-E <: Exception](val i: Int = 0)
+
+@experimental
+object Foo
+
+@experimental
+def bar = 1
+
+
+